This disclosure relates generally to the field of portable illumination devices for illuminating an ambient environment. More particularly, the present disclosure relates to a hand-held laser device that could be used as an effective non-lethal security means, whereby temporary visual impairment reduces a subject's ability to engage in disruptive and/or violent actions.
Methods and devices for producing glare or flashblind effects from a portable visual security device have been disclosed for example, in U.S. Pat. No. 5,685,636 to German, in U.S. Pat. No. 6,190,022 to Tocci et al and in U.S. Pat. No. 6,799,868 to Brown et al. among others. These prior art devices operate by producing radiation at intensities sufficient to dazzle a subject by temporarily reducing visual performance while remaining below levels that can result in permanent damage to the subject's retina.
Generally, to ensure that the device is eye safe, it is an accepted practice that the intensity at the location of the target not exceed, one half the maximum permitted exposure (MPE) value for a particular wavelength. In some cases, the device is expected to meet the requirements of ANSI standard, which allows only 10% of the MPE for a given exposure duration. To comply with this requirement, the devices of the prior art were generally limited to intercepting static targets located at or beyond a certain range, or else they allowed adjustments of the power and/or the beam spread of the output radiation to thereby alter the intensity at the estimated target's location in real time.
Means for changing the beam's spread generally involved controlling the spot size using an adjustable lens contained in the device, as was taught, for example, in U.S. Pat. No. 5,685,636. Alternatively, a fixed beam expanding lens could be disposed in the path of the beam, with the power of the output adjustable up to a maximum specified by eye safety considerations. This realization has the advantage of being adaptable to intercepting moving targets in a variety of scenarios and for a range of exposure times, and could be readily packaged in a compact flashlight type device. It had the further advantage of affording a degree of operational and practical flexibility through utilization of Gaussian beam profiles such as are typically produced by most solid state laser sources, including diodes and diode pumped lasers.
Although effective in certain situations, the laser flashlights and visual security devices of the prior art, including the ones taught in the patents cited above, are deficient in that they could not always provide sufficient power to allow use in certain circumstances. Examples of scenarios requiring greater power than available from existing and prior devices may include operation at higher duty cycles, over longer ranges and/or under adverse ambient light conditions such as clear sunny daylight or in rain or foggy conditions. Even the compact laser flashlight device taught in U.S. Pat. No. 6,799,868 is generally limited to less than about 250 mW at the operational wavelength of 532 nm, due to practical considerations of cost and performance. Power levels available at various other visible wavelengths from diode lasers are typically much lower, especially when TEM 00 outputs are required as well.
Generally, power scaling from a single laser emitter, whether a semiconductor laser or a diode pumped solid state laser (DPSSL) is limited by trade-offs between power consumption properties, resonator design limitations (including thermal lensing), sizing of optical components and the amount of battery power available in a portable unit which can restrict the amount of “on” time and/or duty cycle. Furthermore, the cost of the components tend increase substantially as the power is scaled, putting the device beyond reach for certain security applications. It is therefore desirable to provide a cost effective security device with scalable output power outputs of 1 W and beyond in the visible, while maintaining portability features and effectiveness.